Priming a beer is the process of adding sugar during the bottling process in order to carbonate the beer. You can bottle condition and carbonate your beer by priming it at the time of bottling with a specific amount of sugar. Using approximately .5 teaspoons ( ½ tsp) of priming sugar per 12oz bottle will provide adequate carbonation for most beer styles.
Typically you will want to prime your beer with corn sugar (dextrose). It is critical that your beer completes its fermentation prior to priming and bottling, as residual fermentable sugars can create excessive pressure in the bottles and cause them to explode. It is also critical that the yeast is still viable so that the priming sugar is converted to CO2 in the bottle, and you do not end up with a flat and overly sweet beer. As in all aspects of brewing, cleaning and sanitation is always paramount. Take special care to ensure that your bottles and caps are clean and sanitized prior to bottling.